1. Field of the Invention
The present invention relates to a warm air heater, and more particularly to a forced supply and exhaust type warm air heater.
2. Description of the Related Art
Heretofore, in a forced supply and exhaust (FF) type warm air heater, a combustion fan is disposed in an air supply passage in order to supply combustion air to a burner. The combustion fan is controlled so as to drive at target rotation speed according to the target combustion quantity of the burner, and supplies combustion air quantity according to the target combustion quantity of the burner to a combustion chamber so as to attain an optimum air fuel ratio. Consequently, the combustion state in the combustion chamber becomes excellent.
The density of air taken in the air supply passage from outdoors is different depending on the altitude of the installation location of the warm air heater. Therefore, even when the combustion fan drives at the same rotation speed, the quantity of combustion air supplied to the combustion chamber through the air supply passage changes. Accordingly, a measure to supply the optimum quantity of combustion air to the combustion chamber regardless of the altitude of the installation location, or the like is taken.
For example, Japanese Patent Laid-Open No. 4-227409 discloses an oil fan heater in which an air pressure sensing circuit which senses air pressure of combustion air is provided, and the number of rotations of a burner motor is adjusted according to the air pressure sensed by the air pressure sensing circuit.
Additionally, Japanese Patent Laid-Open No. 2004-163045 discloses that an air damper is selectively installed in an air supply passage according to the altitude of the installation location of a warm air heater, or the air supply passage, when the warm air heater is installed. The air damper is formed with a hole through which combustion air passes, and a plurality of air dampers whose hole areas are different stepwise are prepared.
Furthermore, Japanese Patent Laid-Open No. 2002-317929 discloses a combustion apparatus which comprises a switch which is manually selected according to the entire length of an exhaust pipe, and a switch which is manually selected according to the altitude of an installation location, in which the driving of a blower or combustion gas supply quantity is corrected according to the setting states of these switches.
However, the oil fan heater disclosed in the above Japanese Patent Laid-Open No. 4-227409 needs to be provided with the air pressure sensing circuit which senses the air pressure of combustion air.
In the warm air heater and the combustion apparatus disclosed in the above Japanese Patent Laid-Open No. 2004-163045 and Japanese Patent Laid-Open No. 2002-317929 respectively, an installation worker or the like needs to select and install a proper air damper, or to properly set the switches, according to the altitude of the installation location or the air supply passage.
The present invention has been made in view of the above background, and an object of the present invention is to provide a warm air heater capable of optimizing a combustion state in a combustion chamber, with no additional device provided therein, without setting work or the like by an installation worker or the like, even when the altitude of an installation location is changed.